The release of cardiac Troponin-T (cTnT) as a biomarker of doxorubicin-induced chronic cardiac injury was evaluated in the spontaneously hypertensive rat (SHR) model. Elevations in serum levels of cTnT, and decreased immunohistochemical staining of heart sections for this protein, were noted in SHR treated with cumulative doses of doxorubicin (7 mg/kg) that induced only minimal histological alterations in myocytes. Concentrations of cTnT were further elevated, coincident with reduced immunohistochemical staining, in SHR given 10 to 12 mg/kg doxorubicin. Thus, monitoring serum levels of cTnT can detect doxorubicin-induced myocyte damage in SHR and may prove useful for the noninvasive evaluation of this toxicity in humans.